The present invention relates to a piezoelectric transformer usable in various high voltage power supplies, and more particularly to a piezoelectric transformer scaled down to have a small size and a reduced thickness as well as having high reliability and the ability to generate a high voltage, in addition a packaging method and a packaging structure and furthermore relates to a input and output terminals of the piezoelectric transformer and its circuit interconnection. The high power supply is used, for example, in a deflector for a television system and an electro static charge device for a copy machine. A wound electromagnetic transformer has been used as a transformer for generating a high voltage. The wound electromagnetic transformer has a magnetic core wound with wires. In order to realize a high ratio of transformation, it is required to increase the number of wires wound around the magnetic core. The increased number of wires wound around the magnetic core makes it difficult to realize a small size and thin electromagnetic transformer.
In order to settle the above issue in obtaining both the generated high voltage and the scaling down of the electromagnetic transformer, another transformer has been proposed which utilizes a piezoelectric effect. The piezoelectric transformer has a piezoelectric body with a main face on which electrodes are provided for applications of alternating currents to the electrodes in order to cause a vibration of the piezoelectric body. It is of course important that the piezoelectric transformer is packaged in a molded so as to prevent any disturbance to the vibration of the piezoelectric body. In the Japanese laid-open patent publication No. 7-39912, it is disclosed that the piezoelectric transformer having a spring contact structure. FIG. 1 is a schematic perspective view illustrative of the conventional piezoelectric transformer having the spring contact structure. FIG. 2 is a cross sectional elevation view illustrative of the conventional piezoelectric transformer of FIG. 1.
A piezoelectric transformer 41 is packaged in upper and bottom molded packages 42a and 42b. Namely, the piezoelectric transformer 41 is accommodated in an internal space formed by the upper and bottom molded packages 42a and 42b and is held in the internal space by spring forces provided by upper and lower lead terminals 43a and 43b. The upper lead terminals 43a extend from a side wall of the upper molded package 42a to the internal space. The lower lead terminals 43b extend from a side wall of the lower molded package 42b to the internal space. Top portions of the upper lead terminals 43a have first contact portions 51a. Top portions of the lower lead terminals 43b have second contact portions 51b. The first contact portions 51a of the upper lead terminals 43a are positioned right over the second contact portions 51b of the lower lead terminals 43b. The first contact portions 51a are distanced in a vertical direction from the second contact portions 51b by a distance about a thickness of the piezoelectric transformer element 41 so that the first contact portions 51a of the upper lead terminals 43a are in secure contact with an upper surface of the piezoelectric transformer element 41 by pressing the upper surface downwardly, whilst the second contact portions 51b of the lower lead terminals 43b are in securely contact with a lower surface of the piezoelectric transformer element 41 by pressing the lower surface upwardly. As a result, the piezoelectric transformer element 41 is held by the spring forces provided by the upper and lower lead terminals 43a and 43b. This packaging method is inferior in facilitation of assembling and packaging of the piezoelectric transformer element 41. Top and bottom electrodes 411 and 412 are provided on the upper and lower surfaces of the piezoelectric transformer element 41.
Japanese laid-open patent publication No. 6-6164, discloses that a vibration electronic device is packaged in a molded package. FIG. 3 is a schematic view illustrative of a conventional vibration electronic device packaged in the mold package. A resonator 61 is accommodated in a case 63 with a cap 64. The case 63 is formed with plated wirings 62. The cap 64 is also formed with the plated wirings 62. The resonator 61 is also formed with the plated wirings 62. The resonator 61 is fixed to the case 63 by an electrically conductive adhesive for electrical connection between the plated wirings 62 of the resonator 61 and the case 63 and between the plated wirings 62 of the resonator 61 and the cap 64.
Japanese laid-open patent publication No. 5-243886, discloses that a vibration electronic device is packaged in a molded package. FIG. 4 is a schematic view illustrative of a conventional vibration electronic device packaged in the molded package. A resonator 71 is accommodated in a ceramic case 73 with a ceramic cap 74 via a conductive sheet 72 and a spring terminal 73.
Japanese laid-open utility model publication No. 5-3950, discloses that an electronic device is packaged in another molded package. FIG. 5 is a cross sectional elevation view illustrative of a conventional packaging structure wherein a case is latched to a bottom plate. A molded package 81 has snap fits 84 with latches 82. A bottom plate 85 has through holes 83 so that the snap fits 84 snap into the through holes 83 and the latches 82 of the snap fits 84 latch with the bottom plate 85.
The above described prior arts have the following problems and disadvantages individually.
The first prior art disclosed in the Japanese laid-open patent publication No. 7-39912 has the following problems. In order to allow the lead frames to have a spring force, it is required to provide gaps between the lead frames and the molded package as illustrated in FIG. 2, for which reason the thickness of the package is increased. Further for packaging onto the substrate, there are required processes for folding the lead frames whereby the manufacturing cost is increased.
The second prior art disclosed in the Japanese laid-open patent publication No. 6-6164 has the following problem. The resonator and the wiring are bonded to each other via the electrically conductive adhesive. This bonding structure by the electrically conductive adhesive prevents the resonator from showing vibration. It is further possible that the case and the resonator are bent or arched.
The third prior art disclosed in the Japanese laid-open patent publication No. 5-24886 has the following problem. Since the resonator is held by the conductive sheet and the spring terminal and accommodated in the molded package the thickness of the package is increased.
The fourth prior part disclosed in the Japanese laid-open patent publication No. 6-6164 has the following problem. The latching structure is provided to latch the molded package to the bottom plate. No further function can be obtained.
In the above circumstances, it had been required to develop a novel packaging structure for a piezoelectric transformer free from the above problem.